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240 odometer 200 1986

posted by  wudwagon on  Sat Aug 6 15:31 CST 2005
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First thanks to everyony for responding to my previous post regarding bulb warning indicator switch. Now on to the next problem.

The odometer does not work but the speedometer does. I did a search on the internet and found some instructions to take out the instrument cluster and inspect the odometer gears. upon taking out the cluster and removing the speedometer unit I found that the gear that drives the odometer had a few broken teeth on it and according to my instructions this was probably the root of the problem so I found another site that sold these gears and obtained a new one for $25 + shipping and handling.

I installed the new gear and went for a test ride, the problem was not solved so I took the unit out again and took out the speedometer/odometer and inspected the unit, everything looked mechanically ok, so I put it back together and went out for another test ride around the block and it was still not working.

Next I decided to try an do some troubleshooting on my own, (my chilton's manual does not seem to be very complete in this area) I jacked the rear end of the car up and put the axel on jackstands. With then instrument cluster out I started the car. There are three wires that feed into the speedometer/odometer: red/blk, blk & blue. After taking voltage readings I found 12Vdc between the red/blk & the blk wire and 0 V ac and dc between the blk and blu. I put the car in drive and took readings again. Between the blue and the black there is a an AC signal whose amplitude seemed to be proportional to the speed of the drive shaft starting from 0 VAC at stop and going up as I stepped on the gas. the frequency of that sigal seemed to be around 50 hz at a stop and it increased from there as I took of the brake and pressed the accelerator. I want to assume that this signal is OK and it drives the electronics in the speedometer/odometer unit.

Upon close inspection of the instrument I noticed an IC on the circuit board, it is an ITT UAF 2115. I made the assumption that this chip was the drive for the speedometer and odometer, after some more research on the internet I found this to be correct.

I guess it is possible that this chip could have gone bad, is this a common problem? Should I attempt to replace this driver if it is bad (I am fairly competent in electonics repair) or should I just junk the unit and find a new one?





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